Generally, insulin is used to treat patients, in particular, diabetics for their recovery. The insulin is composed of high polymers with a molecular weight of 6000 or more and has a strong hydrophilic property with peptide bonds of amino acids. Therefore, the insulin is difficult to administer to a body through the epidermis of the skin even if the skin is transformed in properties by chemical solvents.
Also, the hydrophilic insulin is not chemically compatible with the epidermis having a hydrophobic property. For the above reasons, it is known that it is difficult for the insulin to permeate into the skin.
The skin of the body consists of three layers, namely, epidermis, scleroid layer, and derma. The epidermis as outer skin has the least permeation of medical substances and is composed of 2% lipid and 40% protein, and has 0.1 mm or more thickness. The epidermis has a hydrophobic property because each segment of the protein of the epidermis is enclosed with the lipid. Further, in comparison with water contents, those of the derma and the scleroid layer are 70% or more, respectively, and that of epidermis is about 40%. As a result, the epidermis has high electric resistance and protects the derma from heat stimulation and any other external stimulation.
On the other hand, known methods for administering the insulin to the body of the diabetic through the skin are classified into three large types, ointment-type, patch-type, and spray-type. Among the types; the patch-type methods have been actively researched and developed in recent years.
As a prior art, an instrument of the patch-type for administering insulin to the scleroid layer of the skin is disclosed in Korean Patent Publication No. 92-2264, which is incorporated herein by reference. Referring to FIG. 1, showing the above instrument, the instrument comprises a case 1 which stores insulin and solvent therein, a high polymer support 2 which has a water swelling property and on which the insulin is distributed in a powdered state, a skin needle support 3 showing a swelling property in accordance to the discharge of the solvent after the adhesion of the instrument to the skin, a plurality of skin needles 4 which are arranged fixedly and vertically on the support 3 to contact the skin, and an electrode 5 which is provided within the case 5 to apply an electric current.
According to the above configuration, firstly, the instrument is adhered to the skin to bring the needles 4 of the skin needle support 3 into contact with the skin. The, the passages formed by the needles 4 are temporarily closed by the swell of the skin. When the direct current or ripple current is applied to the electrode 5, the ionized insulin and the solvent are moved toward the opposite electrode. At this time, the hydrophilic protein and polypeptide of the skin are parallel and contractedly arranged toward the positive electrode. Thereafter, the passages of the epidermis are opened to permeate the insulin to the derma.
On the other hand, explaining the reason that a plurality of skin needles are used in the prior art instrument, it is that the skin needles penetrate only the epidermis of the skin to permit easy flow of the insulin from the epidermis via the scleroid layer and the derma into the capillary vessels. Therefore, the amount of insulin administered to the body is increased.
However, in the prior art instrument as mentioned above, a plurality of skin needles, are fixedly arranged on the skin needle support which shows the swelling property in accordance to the discharge of the insulin and solvent. Accordingly, it is difficult to make the skin needles of 50 to 400 .mu.m in diameter. Also, the support being formed of materials with swelling property makes the manufacturing cost of the prior art instrument higher.
Further, there exists a problem that the prior art instrument is used only one time because the instrument is not a re-usable single set which comprises a case and a support. Furthermore, generally, thousands of skin needles are required to quickly administer the insulin to the body of the patient. However, hundreds of skin needles may be fixed to the support according to the prior art instrument. Therefore, there are disadvantages that the patient, who adheres the insulin patch to his skin for a long time, feels a pain and must be prudent in his conduct.